Move the command line from cmd/bsdaily into internal/cli (closes #8)

cmd/bsdaily/main.go now only passes Version to cli.Main and exits with
the status it returns, as REPO_POLICIES.md requires of cmd/. The cobra
command, the flag rules and the date parsing moved unchanged into
internal/cli, so flags, help text, error messages, exit status and the
first log line stay as they were. The fallback to dev for an empty
version moved with them into cli.Main.

parseTargetDates is exported as ParseTargetDates so that a table test
outside the package can reach it; the test never touches the filesystem
or runs the extraction. README describes the new layout and TODO.md
records the step.

Model: opus-5-5
Co-authored-by: clawbot <sneak+clawbot@sneak.cloud>

TODO.md

@@ -14,11 +14,15 @@ pre-1.0
 
 # Next Step
 
-Expand tests beyond the compilation smoke test: unit tests for the extraction,
-verification, and atomic-publish paths.
+Expand the `internal/bsdaily` tests beyond the compilation smoke test: unit
+tests for the extraction, verification, and atomic-publish paths.
 
 # Completed Steps
 
+- 2026-10-06: Moved the command line (flags, the rules for combining them, date
+  parsing) from `cmd/bsdaily` into `internal/cli`, with unit tests for the flag
+  rules and the dates; `cmd/bsdaily/main.go` is now a single call into it
+  (https://git.eeqj.de/sneak/bsdaily/issues/8).
 - 2026-10-06: A plain `docker build .` and a host `make` build stamp the git tag
   or short commit into the binary, which `bsdaily` logs on the first line of
   every run and prints with `--version`